Cellular and humoral immune responses against malignant neoplasms are being extensively investigated. Assays of cell-mediated immunity (CMI) fall into three general categories: tests which measure cell-mediated cytotoxicity (CMC), lymphocyte stimulation (blastogenesis), and lymphokine secretion (migration inhibition). Cytotoxicity and blastogenesis assays require tedious maintenance of aseptic culture conditions and may take several days to complete. Migration inhibition assays, while extremely useful in monitoring CMI responses in cancer patients, take 2 days to perform. Furthermore, there are certain difficulties in their quantification. In search of faster and simpler techniques Halliday and Miller.sup.1 introduced the leukocyte adherence inhibition test (LAI). This 1-day assay was based on their observation that some immune lymphocytes lose their ability to adhere to glass surfaces in the presence of specific tumor antigens. In the original method Halliday incubated mixtures of leukocytes and antigens in hemocytometer chambers. The degree of LAI was determined by counting the residual glass-adherent cells after gentle washing. Subsequent attempts to simplify this technique included Holan's tube method and Holt's microplate method. In the tube method, mixtures were incubated in glass tubes and the non-adherent remaining cells in the fluid were counted in hemocytometers..sup.2 Holt et al. incubated in plastic tissue culture plates instead..sup.3 Using these modifications, many workers confirmed Halliday's observation that in addition to cell-mediated reactivities the leukocyte adherence inhibition test can also detect serum blocking factors in patients with advanced stages of neoplasm. FNT .sup.1 Halliday, W. J. and S. Miller, 1971, Int. J. Cancer 7, 1. FNT .sup.2 Holan, V. M. Hasek, J. Bubenik and J. Chutna, 1974, Cell Immunol. 13, 107. FNT .sup.3 Holt, P. D., L. M. Roberts, P. J. Fimmel and D. Keast, 1975, J. Immunol. Methods 8, 277.
Despite these recent advances, LAI as a method for monitoring cell-mediated immunity in cancer patients still has not been extensively used. One of the main drawbacks is that it requires visual enumeration of adherent (or nonadherent) cells. Several hundred cells in each mixture must be counted to obtain reliable results. When large series of antigens or sera are to be tested, the time factor involved can be critical. This severely limits the number of tests that can be run on the same day. For recent modifications of the assay in which cell enumeration has been automated, elaborate instrumentation is required. In 1974 Pierce and Devald.sup.4 introduced an isotopic variant of the LAI assay by labeling rat lymphocytes with technetium 99m in microplates. Although this approach corrected the imprecision of visual counting the short half-life of .sup.99m Tc presented some problems since all tests had to be complete in a few hours. The technique was also laborious and difficult to perform. FNT .sup.4 Pierce and DeVald, Int. J. Cancer 14, p. 833 (1979).
These technical difficulties are further compounded by a lack of understanding of the immunological mechanisms by which the response occurs. While most investigators are of the opinion that there is direct interaction of the leukocytes with tumor antigens there is considerable disagreement on the specific cell types and the exact mechanism by which they are involved. Some have contended that inhibition was mediated by a soluble factor released by sensitized lymphocytes in the presence of specific antigen. Alternative mechanisms thought to be operative under certain circumstances include reactions between antigens and cytophilic antibodies on the surfaces of circulating monocytes and the direct action of antigen on sensitized monocytes. These controversies may be attributed to the fact that most of the studies have been performed with poorly characterized leukocyte subpopulations.